Size (N)

• total # of individuals  in a given area at a given time

• larger size (N)

• safer from population decline

Density

• number of individuals/area

  • Higher density

    • higher competition, possibility for disease outbreak, possibility of depleting food source

Distribution

• how individuals in a population are spaced out compared to each other

  • random: trees

  • uniform: territorial animals

  • clumped: herd/group animals

Sex Ratio

• ratio of males to females

  • closer to 50:50 ideal for breeding

  • die off or bottleneck effect can lead to to skewed sex ratio (not enough females) limiting pop. growth

Density-Dependent-Factors

• factors that influence population growth based on size

• Examples

  • food

  • light

  • competition for habitat

  • water

  • disease

• All these things limit population growth based on their size

Density-Independent Factors

• factors that influence population growth independence of their size.

• examples

  • natural disasters

  • floods

  • hurricane tornado

  • fire

• It doesn’t matter how big or small a pop. is, natural disasters limit them both

Ex. of Density-Dependent Factor

• Food is a density dependent factor. (also a limiting resource)

• When twice as much food was added to the dish, both species increased carrying capacity by about 2x

• Biotic Potential

• Max potential growth rate with no limiting resources

• May occur initially, but limiting resources (competition, food, disease, predators) slow growth, & eventually limit pop. to carrying capacity (k)

Biotic potential

• exponential growth

Logistic growth

• initial rapid growth, then limiting factors limit pop. to K